There are two problems with it. The fact is that it's not alone. The premise is that modern Christianity owes more to secular sources than to the Bible. This is also the idea behind Pagan Christianity, by perennial trend-chasers George Barna and Frank Viola, and as much as I hate to admit it, the latter is the better book.
The other problem is the specter of Open Theism that overshadows the book. For those who don't know, Open Theism is the belief that God doesn't know the future, and it's a position with which Boyd has been increasingly associated. I'm not sure of his beliefs right now, but it's hard not to read his work without that in mind.
Even leaving that aside, I don't recommend it. It's not as good as the book it follows, and it's not as good as the one by Barna and Viola.